The system solution: Fire-rated glazing systems in modern design
Fire-rated glass and awe-inspiring architecture are often seen as an oxymoron in the building and design world. Specified and installed to meet stringent building codes, fire-rated glazing is generally considered a means to an end, not a widely acclaimed design element.
Today’s fire-rated glazing systems are challenging this notion. Developed and tested to work together as part of a comprehensive unit instead of only as individual components, these simple, yet elegant solutions are proving they can satisfy some of the most rigorous building code requirements while advancing modern design. For example, consider the fire-rated curtain wall system in Manhattan’s Fulton Center (discussed in more detail later in this article). Its sleek form wraps around the building’s grand atrium, serving as a barrier to fire while helping flood interior spaces with daylight. It is part of the aesthetic referred to by commuter Dave Palmieri when he told the New York Daily News, “The light pouring in is just incredible. It’s a real modern gem. Spatially, it’s like Grand Central.”
For those considering using fire-rated glazing systems to create design-forward assemblies worthy of such praise, the path to safe and successful installations does not have to be daunting. However, it necessitates a good working knowledge of the performance and design characteristics of today’s offerings, as the material class has evolved significantly in recent years.
A primer on fire-rated glazing systems
To appreciate the significance of modern fire-rated glazing systems, it is important to understand where it all started. Ordinary window glass shatters whenever it is heated beyond 121.1 C (250 F). For decades, traditional, polished wired glass was the only product that could overcome this hurdle and pass the National Fire Protection Association (NFPA) 80, Standard for Fire Doors and Other Opening Protectives, fire test, defending against the spread of flames and smoke (known as fire protection). While its wires appeared to add a level of security, the reality is they were only there to hold the glass in place during a fire. The material was actually a low-impact product and its wires could cause significant harm to occupants when broken.
While building codes typically restrict the use of such glazing in high-traffic areas, the absence of a fire-rated glazing material with the desired impact safety performance led to a code exemption. Building code officials deemed traditional, polished wired glass suitable for use in areas requiring fire protection and high-impact safety protection.
Spurred by injury reports and the need for fire-rated glazing with a more modern aesthetic, manufacturers began developing new solutions. Their efforts led to a sea-change in the industry. Where it was once challenging to think beyond the limitations of wired fire-rated glass, clear offerings with impact safety became the norm. This led the International Code Council to lift the longstanding exemption for traditional wired glass in hazardous locations in the International Building Code (IBC). In 2003, the IBC restricted traditional polished wired glass from hazardous locations in schools, athletic facilities and day care facilities. In the 2006 edition, the restriction was extended to include hazardous locations in all types of buildings. These changes have been upheld in following code cycles, including in the 2018 IBC (see “What Does the Code Say About Impact Safety Today?”).
Although revolutionary, these fire-rated glazing materials were only the starting point for innovation. Continued manufacturing advances led to fire-rated glass and frames with the added ability to defend against radiant and conductive heat transfer (known as fire resistance). These materials conform to the requirements of IBC Section 703, “Fire-resistance Ratings and Fire Tests.” They are tested to the fire-resistance test standards for walls (ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials, and Underwriters Laboratories [UL] 263, Fire-resistance Ratings) and can exceed the traditional size parameters of fire-protective openings, greatly enhancing design flexibility.
With the door open to possibilities, manufacturers began pairing advanced fire-rated glass and frames together as integrated assemblies. From fire-rated glass floors to fire-rated glass curtain walls, there is an ever-growing suite of options available to architects, specifiers and other building professionals.
Understanding the options
Today, building professionals can select from numerous fire-rated glazing systems. The following are some of the most popular offerings on the market.
Fire-rated curtain wall systems
Fire-rated curtain wall systems can provide a substantial area of glazing in interior or exterior locations while defending against the transfer of flames, smoke and radiant and conductive heat. They are tested as a complete system to ASTM E119 and UL 263 (which, as mentioned, are the fire-resistance standards for walls as outlined in IBC Section 703), from the glass and frames to hardware and all component parts.
To achieve the necessary defense, fire-rated curtain wall systems use transparent glass wall panels with significant heat-blocking capabilities. Manufacturers use different methods to ensure these high-performance products pass the necessary fire tests and remain relatively cool on the non-fire side of the glass for the duration of their designated fire rating. One product achieves this outcome by incorporating layers of low-iron float glass with an intumescent interlayer.
Fire-rated curtain wall systems also employ fire resistive-rated framing materials. Some of today’s more innovative systems use steel that has been roll-formed from thin-gauge steel coils. This precise European engineering method results in frames that are narrower than their traditional hollow metal steel counterparts, improving visual integration with non-rated doors, windows and curtain walls.
A supplementary benefit of these next-generation fire-rated steel curtain wall systems is their ability to achieve nearly any finished look. The steel profiles can be powder coated at the factory, while the exterior cover caps can be manufactured from aluminum or stainless steel and then finish matched. If the cover cap is aluminum, it can be painted or anodized. The shape of the cover cap can also be customized; however, this necessitates early involvement with the manufacturer or supplier to ensure all project needs can be met.
Due to recent innovations, fire-rated glass curtain wall systems are also available captured (with a four-sided perimeter frame), with a two-sided perimeter frame or with an uncaptured appearance (achieving the look of a traditional structural silicone-glazed curtain wall system, as discussed in the following section).
Silicone-glazed fire-rated curtain wall systems
Silicone-glazed fire-rated curtain wall systems go a step beyond standard offerings, pairing fire resistance with a smooth glass aesthetic. They make it possible to create dramatic spans of fire-rated glass with clean sight lines and today’s popular frame-free look.
One available assembly achieves this functionality by using fire resistive-rated glass attached to narrow steel fire-rated frames with a toggle retention system. The assembly is then silicone sealed and requires no pressure plates or caps. Once installed, the toggle retention system anchors the glazed lights and becomes completely hidden. On the backside of the system, steel fire-rated frames provide high strength and narrow profiles.
Current silicone-glazed fire-rated curtain wall systems are available with up to 120-minute fire ratings and suitable for interior and exterior use.
Butt-glazed fire-rated glazing systems
Another way to achieve a ‘frameless’ look in areas with stringent fire- and life-safety criteria is through butt-glazed fire-rated glazing systems. They get their visual continuity from using fire resistive-rated glass wall panels that are butt-glazed using silicone sealant. The panels are then secured in place with a heat-resistive perimeter frame.
For more seamless transparency, some manufacturers offer products with vertical butt-glazed joints as narrow as 5 mm (1/5 in.). Additionally, those with a solid multi-laminate glass makeup (such as those with colorless, wireless, low-iron float glass and clear intumescent interlayers) eliminate the need for colored internal spacers between adjoining pieces of glass. They are ideal for interior partitions where purity of color is desirable and can help maintain a strong design intent in spaces where non-rated glazing systems are also allowable.
While the primary appeal of butt-glazed fire-rated glazing systems is their predominant glass presence, manufacturers still consider the appearance of the perimeter frame. It can typically be customized to suit design needs or minimized by varying the configuration.
Fire-rated glass floor systems
System solutions are not just limited to vertical applications with fire-rated criteria. The last decade has given rise to fire-rated glass floor systems. They are available for areas requiring a code-approved fire barrier between building levels, allowing daylight to be shared between floors while providing critical compartmentation in open, lofty interiors.
First-generation fire-rated glass floor systems use a steel framing grid, which is anchored to load-bearing materials, to separate the fire-resistive glass from the tempered, laminated walking surface glass. This effectively preserves the integrity of the rated material. It also allows it to support structural loads while defending against fires. Current offerings are tested in accordance with ASTM E119, UL 263 and NFPA 251, Standard Methods of Tests of Fire Resistance of Building Construction and Materials, and are available with fire ratings of up to two hours.
Depending on the application, design professionals can select from fire-rated glass floor systems that can support live loads up to 732 kg/m2 (150 psf). Floors with this load capacity are suitable for applications with frequent pedestrian use. The walking surface treatment can be customized to meet the U.S. Occupational Safety and Health Administration (OSHA) minimum requirement for slip resistance (static coefficient of friction [COF] of 0.50), as well as the minimum set under ANSI A137.1, Tile Slip Test (0.42 dynamic coefficient of friction [DCOF]).
Basics and best practices
Fire-rated glazing system use is not as complicated as one would think. However, as it involves a specialty material, some of the steps may seem challenging for those who do not regularly work with these types of systems. To help simplify the process, one should consider the following tips.
Verify a system’s approach makes sense
Fire-rated glazing systems can provide a number of benefits. However, they are better suited for certain types of projects than others. Projects for which they make sense are ones in which:
- the application must defend against the transfer of flames, smoke and heat;
- the assembly is expected to exceed 25 percent of the total wall area;
- visual continuity with non-rated systems is integral to the success of the project;
- it is crucial to bring daylight deep with a building’s core; and
- fire-rated glazing with multi-functionality is required.
Use the supplied materials and install to the manufacturer’s installation manual
A primary benefit of fire-rated glazing systems is the assurance the entire unit or elevation meets code requirements. All components are designed and tested in the same assembly to the same standard, resulting in a tested and listed system. This is a critical safeguard since the IBC requires all elements — from the frame to the glass, seals and other components—to provide the same type of fire protection (e.g. fire resistance or fire protection) and carry the minimum fire rating as stated in the code.
In application, this often means the product configurations and details shown in manufacturers’ literature may be the extent of the available standard selection. It is important to use all supplied components and install the tested and listed system in accordance with the installation manual. While it may be tempting to swap out a system component with an ‘equal’ product to meet project needs or achieve a different price point, it can place the entire assembly at risk and jeopardize code compliance. For example, if the substituted material has not been approved for use through testing, the frames and glass may not provide the level of intended fire protection performance.
Consider all the application requirements
Many fire-rated glazing systems are required to do significantly more than stand guard against fire, whether it be visually matching an adjacent system, transmitting daylight or delaying forced entry. The demand for multi-functionality is a key reason why it is crucial to ensure the selected fire-rated glazing system meets all performance requirements. One of the most common demands is impact safety.
As stated earlier, as of the 2006 IBC, fire-rated glazing in hazardous locations must pass an impact safety test. This includes all fire-rated glass in doors. It also typically applies to fire-rated glazing adjacent to or near the door, including sidelites or glass located near the floor. A comprehensive list of all hazardous locations is outlined in Section 2406, “Safety Glazing,” of IBC 2018 (see subsection 2406.4, “Hazardous locations”). As such, it is important to verify the selected offering meets either Consumer Product Safety Commission (CPSC) 16 Codes of Federal Regulation (CFR) (Category I) or CPSC 16 CFR 1201 (Category II) impact classifications, as determined by the application. Category II is the highest level of impact safety, representing 7.2 kN/m2 (400 ft/lb) of impact. Category I meets 19 kN/m2 (150 ft/lb) of impact. Today, numerous products meet Category II criteria. Some have the additional capability to provide supplemental security protection, such as bullet and hurricane resistance.
Involve the manufacturer early in the design process
Conversations during the initial stages of a project are crucial since they can help the manufacturer or supplier better understand project goals, from long-term performance to aesthetics and cost. This leaves time for manufacturers to address questions, provide application options, and assist with any creative problem solving.
Early involvement is also critical from a material delivery and scheduling standpoint. Fire-rated glazing is a specialty material and may require additional time for delivery. However, with appropriate planning, fire-rated glazing systems can be delivered or phased to integrate seamlessly with the installation team’s needs.
What does the code say about impact safety today?
The 2018 International Building Code (IBC) provides standards for impact loads, required impact tests and hazardous locations for glass. Since Section 2406.1 (Human impact loads), Section 2406.2 (Impact test) and Section 2406.4 (Hazardous locations, sub-sections 1 through 7) do not list wired glass as an exemption, traditional wired glass is not allowed in safety impact areas. Three relevant sections of the code read as follows:
Section 2406.1 Human impact loads: Individual glazed areas, including glass mirrors, in hazardous locations as defined in Section 2406.4 shall comply with Sections 2406.1.1 through 2406.1.4.
Section 2406.2 Impact test: Where required by other sections of this code, glazing shall be tested in accordance with CPSC 16 CFR Part 1201. Glazing shall comply with the test criteria for Category II, unless otherwise indicated in Table 2406.2 (1).
Section 2406.4 Hazardous locations: The locations specified in Sections 2406.4.1 through 2406.4.7 shall be considered specific hazardous locations requiring safety glazing materials.
Close up: The Fulton Center
Located in the Lower Manhattan Financial District, the 16,700-m2 (180,000-sf) Fulton Center integrates five subway stations served by nine different lines and includes retail and office space.
A defining visual feature of the building is a 16-m (53-ft) diameter glass oculus (Latin for ‘eye’), which streams light into a grand atrium. Beneath the oculus is the ‘Sky Reflector Net,’ an artwork by James Carpenter Design Associates, Grimshaw Architects and Arup with 952 perforated aluminum panels that transmit sunlight 34 m (110 ft) down into the Fulton Center’s lowest levels.
Within the atrium is a two-level circular enclosed space that will house restaurants and retail. As it matches the curve of the oculus, some members of the project team affectionately call this space the “doughnut.” To keep with the light-filled aesthetic of the rest of the Fulton Center, the designers wanted this space to be glazed to allow in light from the oculus and Sky Reflector Net.
Designing and installing the glazed curtain walls for the doughnut required overcoming several complexities. In addition to its curved form, the doughnut’s walls also slant upward to match the angle of the oculus, which creates an inverted plane. To successfully achieve this design, the manufacturer worked with the project team to develop custom captured horizontal steel mullions that fit the distinctive shape for a flush and plumb surface appearance, with adequate spacing between each curtain wall segment.
Another challenge of the project was matching the aesthetics of the fire-rated curtain walls on the doughnut’s upper level and in a prominent elevator core with the non-rated curtain wall system on the doughnut’s lower level. To achieve a seamless aesthetic, the designers chose matched curtain wall systems.
The steel frames were formed from tubes instead of sheets and shaped in an extrusion-like process allowing for a wide range of narrow mullion profiles. Since the same manufacturing method can be applied to fire-rated frames using steel back members, it was possible for the fire-rated curtain wall to match the slender frame profiles of the non-rated system.
“Since the interior spaces are flooded with light, a crucial part of the design aesthetic was glazed curtain walls with clean sight lines,” said Andrew Anderson, associate principal with Grimshaw Architects. “That’s easy enough to achieve with non-rated curtain wall assemblies, yet the fire-rated curtain walls provide the same crisp, modern look.”
Conclusion
While one of the primary advantages of selecting a fire-rated glazing system is its ability to bring form in line with function, aesthetic goals should never come at the cost of safety. Manufacturers and suppliers are available to help problem solve and work with the design team to balance life safety with design goals.
